Abstract
Although many Westslope Cutthroat Trout Oncorhynchus clarki lewisi populations in Idaho are robust and stable, others are depressed. In some systems, such as the South Fork Clearwater River (SFCR) system, environmental conditions (e.g., summer temperatures) are hypothesized to limit populations of Westslope Cutthroat Trout. Radiotelemetry and snorkeling methods were used to describe movement, distribution, and habitat use of Westslope Cutthroat Trout in the SFCR in 2013 and 2014. Sixty-six tags were implanted into fish (155-405 mm). Sedentary and mobile summer movement patterns of Westslope Cutthroat Trout were observed. Sixty-two sites were snorkeled along the mainstem SFCR from 5-14 August 2014 to better describe the distribution of Westslope Cutthroat Trout. Twenty-three Westslope Cutthroat Trout were observed in 12 sites and at low densities (mean ± SD; 0.0003 ± 0.0008 fish/m2). Results indicate that summer temperature was the primary factor limiting the distribution of Westslope Cutthroat Trout in the system.